The modem practice of ion mobility spectrometry (IMS) normally involves ionization processes centered on the use of a radioactive 63Ni or 3H source, typically foil. Aside from the fact that the radioactive source has logistical problems in documenting control and safety of the source, including licensing issues and transport of apparatus using the radioactive source into foreign countries, this type of ionization device relies upon gas phase processes to effect ionization. Therefore, particulate matter is analyzed after a transfer of analyte ions from the particulate to the gas phase, typically by thermal desorption/vaporization, as is the current popular practice.
Another drawback to the current technology in ion mobility spectrometry (IMS) and atmospheric pressure ionization (API) mass spectrometry is that typically the sample particulate needs to be vaporized before introduction into an ionization source, leading to potential thermal degradation of analyte ions and increased instrument complexity in the way of controls and space requirements for both ionization and vaporization elements. In addition, IMS instruments require that an ion gate be placed in front of the drift tube in the spectrometry analyzer to control the flow of ions into the drift tube. Ion gates are fragile and, thus, affect the ruggedness of an instrument containing such a device. Additionally, ion gates require the addition of complex electronics to drive gate pulses, increasing the cost of IMS instruments.
Since the resurgence of IMS as a technique for field use for applications such as the detection of explosives and other contraband in airports, there has been an increased need to have an inexpensive, robust IMS apparatus available for such use. It is also desirable to have a atmospheric pressure ionization mass spectrometer which does not rely on thermal desorption/vaporization prior to the introduction of analyte ions to the detector.
The use of a electrospray device in mass spectrometry is known as a means for ionizing and vaporizing a sample prior to introduction into the spectrometry analysis section, but such use is limited to mass spectrometers which operate under a vacuum. Further, the liquid transfer medium for carrying the sample into the electrospray device presents a substantially different system than the gas carrier fluid systems used in IMS and API spectrometry.
Therefore, what is needed is a rugged, efficient, non-radioactive method and apparatus for vaporizing and ionizing sample particulate in IMS and API spectrometers.